The impact of perceived self-connection on possession-based placebo analgesia : an investigation using implicit and explicit measures

Previous study found merely possessing a placebo analgesic cream (without using) has similar pain outcomes when it is compared with using a placebo analgesic cream, but the underlying mechanism is unclear (Yeung et al., 2019). Yeung et al. (2020) proposed that an object-to-self expectancy can be a possible mechanism underlying a possession-based placebo effect, which means people believe that the owned object will benefit them. The present study aimed to examine this hypothetical mechanism and investigate how forming a cognitive connection between the analgesic cream and the self affects the possession-based placebo effect. We demonstrated the effect existed and observed how an explicit self-object association (high vs. low) affects pain outcomes (Study 1), and the implicit nature of self-object association tendency (Study 2). In Study 1, participants were randomly assigned to either the experimental (EXP) conditions (EXP1: possessed a placebo analgesic cream with high self-object connection; EXP2: possessed a placebo analgesic cream with low self-object connection) or control (CO) conditions (CO1: possessed a pain-irrelevant cream; CO2: no-possession). Participants in EXP1 and EXP2 were manipulated to form a high or low cognitive association with the analgesic cream. All participants completed a cold pressor test (CPT) and their pain outcomes were recorded such as pain threshold, pain tolerance, and pain intensity. Our study 1 results showed a significant difference between EXP1 and EXP2, which means the manipulation task was successful. Also, EXP1 condition showed significantly better pain outcomes (participants enjoyed higher pain threshold and longer pain tolerance) than the other three conditions (EXP2, CO1 and CO2), while no significant differences were observed among EX2, CO1 and CO2. Thus, Study 1 suggested merely possessing a placebo analgesic with high perceived self-connection enhances pain experiences. In Study 2, participants were randomly assigned to either EXP condition (possessed a placebo analgesic cream) or CO condition (no-possession). An implicit association test (IAT) was designed to measure whether there is an implicit cognitive association between the self and the owned object after people owned (vs. not own) the analgesic cream. All participants underwent a CPT. Results showed that participants in the EXP condition reported higher levels of object-to-self expectancy and experienced greater placebo analgesic than those in the CO condition. Additionally, the IAT results indicated that participants who merely possessed an analgesic cream were more likely to form an implicit association with it. In conclusion, our study investigated an implicit and explicit self-object association underlying a possession-based placebo framework. The findings suggest that a strong explicit self-object association can enhance placebo analgesia, and there is a possibility of an implicit self-object association existing within the context of possession-based placebo effects.